The present invention relates to spray painting devices; more particularly, the invention relates to a device for the electrostatic spraying of conductive, water-base liquids.
The technique of electrostatic spraying is well known, wherein a high electrostatic voltage is used in association with a spray gun in order to develop electrostatic charges on the sprayed liquid particles. The charged particles become strongly attracted to an article which is maintained at an electrical neutral voltage, and a high percentage of the particles which are sprayed actually land on the surface. This technique greatly reduces overspray and reduces the problems associated therewith, including the problem of environmental pollution.
Electrostatic spraying becomes more difficult when conductive liquids are sprayed, as for example water-base paints. Under these conditions, the electrically-charged paint particles are still needed for spray coating applications, but the conductive liquid column which moves through the spray system tends to short circuit the voltage to ground, and thereby interrupt the voltage-charging capability of the system. This problem has been dealt with in a number of different ways in the past, including using a peristaltic-type pump for voltage isolation, as is disclosed in U.S. Pat. No. 4,982,903. Another approach has been to electrically isolate all components associated with the liquid column, including the liquid container which holds the supply of liquid to be sprayed. These approaches necessarily complicate the construction and operation of such system, and tend to create a hazardous workplace. Examples of system constructions where insulated components have been used in an electrostatic spraying system include U.S. Pat. No. 4,879,137, issued Nov. 7, 1989; U.S. Pat. No. 5,083,710, Jan. 28, 1992; U.S. Pat. No. 5,094,389, issued Mar. 10, 1992; and U.S. Pat. No. 5,096,126, issued Mar. 17, 1992.